As a technique relating to head-up display apparatus, Patent Literature 1 discloses the arrangement “that includes a translucent liquid crystal display panel, a backlight for backlighting the liquid crystal display panel, and a projection optical system for enlarging and projecting an image displayed on the liquid crystal display panel. The projection optical system includes relay lenses and a projection lens. The relay lenses are arranged to utilize telecentric display light with high efficiency if several conditions are met, so that the image displayed on the liquid crystal display panel is enlarged to form a real image. The real image is further enlarged and projected on the windshield of the automobile by the projection lens, displaying a virtual image for the driver (excerpts from the abstract).”
Further, Patent Literature 2 discloses the arrangement “that includes an image formation element that forms an image to be displayed and an optical element that causes a virtual image to be displayed by reflecting light emitted from the image formation element. The optical element has a shape concave toward the direction of travel of the light emitted from the image formation element. The optical element also directly receives the light emitted from the image formation element without being reflected by another optical element. Further, the image formation element is arranged approximately at right angles to the direction in which the virtual image is perceived through the optical element (excerpts from the abstract).”